High-pressure cleaners of the kind referred to above are known, e.g. from European patent application No. 420,473. Experience has shown that in certain cases and under certain operating conditions, combustible or gas mixtures may form in the space within the housing not occupied by the electric drive motor and possibly at least part of the pump or the latter's drive mechanism. Thus, cases of violent combustion have occurred, causing damage to or deformation of the parts surrounding the space occupied by the combustible gas mixture. It appears that in some cases, the phenomena are caused by oil having seeped through worn seals from the pump, or by chemicals or solvents in the electric drive motor being driven out when the motor becomes hot during operation of the cleaner, the gas being ignited by sparks from the motor's commutator. Thus, in most cases, there is a risk that such rapid combustion may occur with the consequent risk of damage to the cleaner and of the operator being at least scared by the noise.